def定义的函数怎么把它画出图

Question

import numpy as np
import matplotlib.pyplot as plt
from scipy.interpolate import make_interp_spline
import numpy as np
R,F,q = 0,0,0
a = 0
l = 0
xd,xq,xw = 0,0,0
xf = 0
D,W = 0,0
yn_ = 0
xn = 0
def x(y): # print(a, y)
x = y / (a - (a - 1) * y);
return x;
def yn1(xn):
yn1 = (R / (R + 1)) * xn + xd / (R + 1);
return yn1;
def yn2(xn):
yn2 = ((l + q * F) / (l + q * F - W)) * xn - W * xw / (l + q * F - W);
return yn2;
等等